Tissues in the Crustacean Limb. sia Eg 
jet of blood from the exposed stump, and then a slight bulging of the 
tissues over the surface of the stump with no further escape of blood. 
The location of the two venous channels could be distinguished quite 
readily by the transparency of the now turgid valves closing each 
lumen. The two valves were then gently pressed inwards with the 
tip of a pencil and in each case, a slight opening of the valve being 
effected, there at once followed a jet of blood. The valvular function 
of these folds seems, therefore, to be clearly demonstrated. 
This description may be summarized with the statement that a 
septum of connective tissue extends across the cavity of the limb 
in such a way as to divide the venous sinus into two channels in 
its passage through the breaking joint. Through this septum and the 
adjacent connective tissue pass the two arteries and nerves. Proxi- 
mally the septum forms two folds which function as valves for the 
venous channels. 
It can readily be appreciated how in previous descriptions some 
of the relations of these structures may have been overlooked. For 
when the valves have closed after autotomy, the remaining stump 
presents every appearance of a continuous membrane extending over 
its exposed surface, ‘‘perforated only by a nerve and a blood vessel,” 
so that in the following statement Fredericq (’92) even indicates 
a doubt regarding the passage of the vein, “Seul le nerf mixte de la 
patte, V'artére (et un sinus veineux?) franchissant cette limite et 
passent du basipodite dans Vischiopodite, 4 travers un orifice étroit, 
creusé dans la membrane obturatrice” (p. 177). 
e. An Embryonic or Transitory Muscle-—Both Fredericq (792) 
and Morgan (’00) have recorded the fact that in the chela of the 
adult crayfish or lobster “no muscle passes from the ischiopodite to 
the basipodite”’. In other words, in the adult lobster no muscle 
extends across the breaking joint. It was with considerable surprise, 
therefore, that it was found that this is not true for the larval lobster. 
In the study of sections of the chela of larval animals, a well devel- 
oped muscle was discovered extending from the ischiopodite to the 
basipodite, and consequently passing through the breaking joint. 
This muscle is easily seen in a longitudinal section of the limb (Fig. 
5, m). It is attached to the inner side of the ischiopodite, passes 
